fix(nxls): add project folder tree e2e test & only track children by dir

[MaxKless]

• adds an nxls e2e test for the project folder tree used to render the projects view/nx toolwindow sidebar
• reworks the project folder tree to only track each node's children as strings vs. duplicating the entire node every time -> approx. 3-4x reduction in size on the nx repo, good for memory usage on large repos

[nx-cloud[bot]]

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